1. FIELD OF THE INVENTION
The present invention relates to extrusion blow molding machines for providing blow molded containers and other hollow articles. More particularly, the invention relates to an accumulator head for an extrusion blow molding machine wherein plasticated material is received in a tubular accumulator and is then extruded through an outlet die to provide a tubular parison from which the bottle or other hollow article is thereafter formed by blow molding.
2. DESCRIPTION OF THE RELATED ART
Containers and other hollow articles are frequently formed by blow molding, which involves providing a tube of heated and softened plastics material about which a two-piece mold is enclosed, after which air or other gasses are introduced under pressure into the tube to expand it against the walls of the mold to thereby form the desired hollow article. Such blow molding machines can be of various types, the most common of which are extrusion-blow molding machines and injection-blow molding machines.
In extrusion-blow molding machines, plastics material is heated and softened in an extruder and is conveyed into a die head from which a tubular parison is extruded. The parison can either be continuous, whereby a plurality of molds are sequentially enclosed about successive, axially spaced portions of the parison, or individual parisons can be intermittently extruded and subsequently blown. In the latter instance, the die head includes a chamber, usually called an accumulator, in which the extruded material is accumulated to provide a predetermined volume of material, after which the accumulated volume of material is extruded through an extrusion die at the outlet of the accumulator to form a parison having the desired length, diameter, and wall thickness distribution.
Most often, the extrusion head is so oriented as to cause the parison to be extruded downwardly in a substantially vertical direction. Additionally, the heated and softened plastics material is normally provided by a screw-type extruder that is disposed horizontally, and the output from the extruder is discharged horizontally into the extrusion head. Because the extrusion head includes a central cylindrical mandrel to control the flow of material through the accumulator outlet or extrusion die, the horizontally entering material must separate and flow around the cylindrical mandrel and then recombine to permit the material to flow in an annular flow path along the mandrel and toward the extrusion die outlet. Oftentimes, the material does not intimately join together as it flows around the cylindrical mandrel to recombine, thereby resulting in the formation of a joint or flow line that can result in a longitudinal surface line or ridge on the extruded parison. Such a line or ridge on the parison can affect the appearance or quality of the blown article.
It is therefore an object of the present invention to overcome the shortcomings described above.
It is another object of the present invention to provide an accumulator head in which incoming extruded material is divided into a plurality of streams that are then recombined to provide a uniform annular flow of plasticated material to provide a circumferentially uniform extruded parison.